Existing methods of spectral examination of biological tissues and other turbid media are often less than desirable. These methods fail to properly normalize for variations in the density, scattering, reflectivity, absorbance and transmittance of such tissues and as a result, have wide variations in the results obtained. Typically, spectral transmittance, fluorescence (normal and time resolved) and Raman spectroscopy are used to evaluate biological tissues and other materials in order to determine the materials present and measure their concentrations. Each of these methods are affected by the scattering, reflecting, absorbing and transmitting properties of the media since the amount of light reaching the tissue is a function of these parameters and in the case of fluorescence and Raman emissions, reabsorption of emission spectra.
In our pending patent application Ser. No. 07/731,533, we discussed the use of new normalization techniques for the detection of cataracts and diabetes. In addition, we are aware of a patent by Schiller, German Patent #261957A1 and R. R. Alfano, U.S. Pat. No. 4,930,516 (which patents are incorporated herein in their entireties by this reference), which refer to the use of the ratio between two fluorescence peaks in fluorescence spectroscopy as normalization techniques. However, since both the target spectra and the reference spectra are affected by scattering and absorption, these techniques are not wholly satisfactory.